This invention relates to a lowering collision avoidance device of a crane. More particularly, the invention concerns the device useful when applied to a container handling crane installed in a container yard such as a port yard.
In a container yard such as a port yard, containers transported there by a chassis, an automated guided vehicle (AGV) or the like are handled, one by one, by a container handling crane installed in the container yard so as to be stacked in layers (on other containers) or placed on the floor (lowered onto the ground) in the container yard.
FIG. 6 is an explanation drawing showing the constitution of a conventional container handling crane. As illustrated in this drawing, the container handling crane has a structure comprising a girder 1 provided horizontally above a container yard, legs 2 supporting the girder 1, and running systems 3 provided at the lower ends of the legs 2, as well as a trolley 4 mounted on the girder and running along the girder 1, a hoisting/lowering device 5 mounted on the trolley 4, a hoisting/lowering drive motor 7 for driving the hoisting/lowering device 5, a rope 6 taken up or paid out by the hoisting/lowering device 5, a hoisting accessory 10 suspended from the hoisting/lowering device 5 via the rope 6, and a rope winding speed controller 20 for controlling the hoisting/lowering drive motor 7.
In placing a container 11, for example, at a target position 12 (on a container 21) between adjacent containers 22 and 23 stacked high in layers, the container handling crane acts as follows:
When a chassis or AGV 30 bearing the container 11 stops beside the container handling crane, the trolley 4 is moved along the girder 1 and halted directly above the chassis or AGV 30.
Then, the hoisting/lowering device 5 is driven by the hoisting/lowering drive motor 7 to pay out the rope 6, thereby placing the hoisting accessory 10 on the container 11. The container 11 is held by a twist lock mechanism (not shown), and the rope 6 is taken up by the hoisting/lowering device 5 to lift (hoist) the container 11 together with the hoisting accessory 10.
After or simultaneously with hoisting the container 11, the trolley 4 is moved along the girder 4. After or simultaneously with moving the trolley 4, the rope 6 is paid out by the hoisting/lowering device 5 to move down (lower) the container 11 along with the hoisting accessory 10 and bring it to the target position 12.
In other words, when the container 11 is to be carried to the target position 12, the container 11 is hoisted once to a higher position in order to escape a stack of containers lying in the way. During or after this hoisting, the trolley 4 is moved to a targeted position above the container 21. While or after moving the trolley 4, the container 11 is lowered to be put to the target position 12.
During the foregoing process, the container 11 is suspended by the rope 6, and so moves while swinging horizontally under the influence of the wind or changes in the speed of the trolley 4. To reduce the amount of swing of the container 11, various ideas have been incorporated, such as the provision of an auxiliary rope or the use of a method for automatically controlling the acceleration of the trolley 4. However, as long as the container 11 is suspended by the rope 6, it is impossible, in principle, to eliminate the swing of the container 11 completely. Particularly in a strong wind, its swing is marked.
Thus, when the container 11 is to be lowered to a place where the containers 22, 23 are stacked high in layers in adjacent rows as shown in FIG. 6 (i.e., to the target position 12), there is a possibility that the container 11, while being lowered, will collide with a container in the adjacent row particularly when a strong wind is blowing. A collision, if any, may cause damage to the container or its fall.
To avoid this accident, customary practice has been as follows: When lowering a container to a place where containers are piled high in layers in adjacent rows, namely, during its intrusion into a canyon, an operator reduces the container lowering speed, and performs an operation while making sure that this container does not collide with the adjacent container. If the container swings markedly and may collide with the adjacent container, the operator terminates its lowering immediately.
This conventional method, however, posed the problem of taking time for lowering the container, making it impossible to shorten the cycle time.